This invention relates to the hot-dip metal-coated steel tube production system consisting of an electric seam-welded tube production equipment wherein steel strips are worked into tubes through a forming roll and a hot-dip metal-coating device.
In such a production system, high quality tubes can be produced at the cost as low as 2/3 to 1/10 of that by the conventional gas welding or low-frequency electric welding process, and at the same time, they can be coated with the molten metal. For this reason, the hot-dip metal-coated steel tube production system insures higher production with high efficiency than the conventional two processes individual production method.
In a high-frequency induction welding process, the saturated magnetic flux density is considered to be raised for a higher welding speed by inserting ferrite cores into tubes to be welded together. This saturated magnetic flux density sharply drops, if the ferrite core temperature exceeds a certain temperature, for example, 180.degree. C. Consequently, the cores should be cooled to prevent a rise in their temperature. In the current method, the cooling water is supplied into a core assembly case containing ferrite cores from its one end. This cooling water is discharged from the other end of the said case toward the inner surface of a welded pipe. In the present integrated production system wherein the molten metal coating is effected immediately after the high-frequency induction welding process, however, cooling of the cores with liquid is practically very dangerous because of a possibility of such an accident as explosion caused by contact of the cooling water with the molten metal due to an unsatisfactory welding practice.
Further, in the integrated production system, the pipe inner surfaces are painted in the subsequent process and therefore, if the cooling water is used as stated above, a special drying process is required, resulting in the increased equipment cost and in the complicated production process.